Degradation of lac with storage and a simple method to check the same

The purpose of this paper is to find out a convenient chemical treatment for seedlac and shellac (semi‐refined and refined commercial forms of natural resin lac, respectively) for preventing degradation during storage at room temperature condition.

Seedlac and shellac are treated with a dilute solution of an antioxidant before storage. This method has not been attempted before. The changes in the physico‐chemical properties of both untreated and treated resins are investigated periodically during storage.

Antioxidant delays the degradation of seedlac and shellac at least by six to eight months during the early period of storage. It is further observed that oxalic acid, used in the trade during conversion of seedlac into shellac by hot filtration for imparting gloss on shellac flakes for attracting buyers), causes rapid polymerisation of shellac resulting in zero value (100 percent decrease) of flow (fluidity) within 30 months of storage, whereas, shellac prepared without treatment of oxalic acid could be stored beyond that period without a significant deterioration in its qualities.

Antioxidants are known to be scavengers of OH groups. Lac resin (shellac and seedlac) contains five hydroxyl groups and one carboxyl group. Thus, only one dilute concentration of antioxidant is used to avoid possible modification of seedlac and shellac.

Consumers of shellac are not aware of the ill effect of oxalic acid treatment being practiced by processors. The results obtained in the present study will help consumers to advise processors suitably before purchase and will be able to store shellac for a longer period if it is not treated with oxalic acid. The consumers may also use an antioxidant to delay degradation of seedlac/shellac.

The results obtained in this paper, regarding the effects of treatments of antioxidant and oxalic acid are not available in any previous publication. These are reported for the first time.